If you are a UK resident, you need to declare all the incomes to the HM Revenue & Customs including revenue from google adsense, ebay, and etc. If your total income is below personal allowance, you do not need to pay tax. The personal allowance for each tax year differs. For 2012-13, it is £8105, i.e. You only need to pay tax on the amount that exceeds £8105. For more about income tax rates and taxable bands, you can check here.